Modelling the effect of cultivation on the dispersion of pollutants in soil

This is a case-study of non-linear modelling in environmental statistics. In a long-term agricultural experiment, pollution of soil by heavy metals from sewage sludge appears to decrease over time. This is explained by cultivation activity which disperses the pollution outside the treated plots. A two-dimensional diffusion model is adapted to quantify the rate of dispersal and is fitted to series of samples taken across the experiment. This demonstrates that most of the original pollution is still present in the soil. The effect of serial correlation of the observations is investigated but found not to affect the results.